1. Field of the Invention
The present invention relates to a heat treating apparatus which is suitably used for, for example, a film forming apparatus.
2. Description of the Related Art
As the technique for forming a wiring layer or layers by depositing a metal or a metal silicide film on a semiconductor IC formation circuit, use has long been made of a PVD (physical vapor deposition) method, such as vapor deposition and sputtering. In those integrated circuits, such as VLSIs, a wiring pattern is more and more microminiaturized so as to achieve a high-speed device in a high integration density. However, a poor step coverage occurs over the uneven surface of a semiconductor device, when the PVD method is employed in the manufacture of that device, resulting in the malfunction of elements or in an increased resistivity.
In an apparatus for depositing a silicon film on a semiconductor structure, a batch type hot-wall furnace has been primarily employed. However, a stricter requirement has to be met in order to eliminate a problem of contamination resulting from an entry of an outer atmosphere and to form more and more thin film on the semiconductor structure so that a semiconductor integrated circuit is microfabricated in a high integration density. In recent times, attention has been paid to a growth technique in which a film is formed over a substrate to be treated, by a single wafer-fed CVD (chemical vapor deposition) method, in a vacuum load-lock chamber-equipped apparatus through a reaction of a feed gas by the use of heat, light or plasma.
The single wafer fed CVD film growth method ensures a better step coverage over that of the PVD method and imparts no damage to a substrate to be treated and, as compared with a batch type CVD, involves no entry of an outer atmosphere into a reaction chamber due to the presence of a vacuum load-lock chamber. It is also possible to readily control a film thickness and film quality.
In this type of single wafer-fed CVD film growth method, as shown in FIG. 1, a substrate 1 to be treated is placed in contact with a heating body, such as a chuck or susceptor 2, and heated to a temperature conforming to a film formation. The heating body, such as the susceptor 2, is heated by a heating source 3, such as lamp light and resistance heat-generation heater, and serves as such. In this case, the temperature of the susceptor 2 or substrate 1 is monitored by a temperature monitor means, such as a thermocouple and radiation thermometer, and the monitor means controls the temperature of the substrate 1 during the formation of a film.
Upon a detailed examination by the inventors, it is found that the heat conduction problem arises in the conventional film apparatus at a location between the susceptor 2 and the substrate 1 and that, even if the substrate 1 is placed in contact with the susceptor 2, no equal temperature is achieved on the susceptor 2 and substrate 1, for example, the substrate is lowered in temperature to 550.degree. C. when the susceptor is at 680.degree. C. This is because, even if a flat contact state is visually observed between the rear surface of the substrate 1 and the mating surface of the substrate 2, it appears uneven microscopically as a point-contact state as shown in FIG. 2. Stated in another way, under a reduced-pressure condition particularly under which there is less gas conducible to the conduction of heat, the way of heat conduction is different from that under an outer atmosphere condition.
In the CVD method, a film is formed on the surface of the substrate 1 through the decomposition of a feed gas by heat, light or plasma in the course of a reaction in which case the decomposition and reaction of the feed gas rely largely on a temperature involved. In the treatment state as shown in FIG. 1, an exposed surface portion 2a of the susceptor 2 is higher in temperature than a temperature prevalent on the major surface of the substrate 1, causing the decomposition of the feed gas to be more actively done at the exposed surface portion 2a of the susceptor 2 than at the major surface of the substrate 1 in the course of a reaction. For this reason, the feed gas to be decomposed on the outer marginal portion, in particular, of the substrate 1 is deprived of by the exposed portion 2a of the susceptor, causing the film thickness to be thinner on the marginal portion of the substrate 1 than on the central portion thereof. This poses a problem of impairing the uniformity of a film thus formed under the condition as set out above.